It is generally known that extraction methods and equipment for so-called heavy beds in a single process are gaining increasing interest. Attention of the experts is focussed mainly on processes and equipment for the sublevel caving.
Two systems are distinguishable in sublevel caving technology. In one of the systems the equipment has an opening on the sloping back towards the caving-side end, through which the coal can be forwarded to a second conveyor around the central part of the equipment. The first conveyor is at the face-side part of the equipment and its purpose is to carry off the coal extracted by the power loader at a continuous rate. Owing to the two conveyors, such equipment is expensive and the operation and repair require significant cost. The fact that the opening available for the sublevel caving is small represents an additional disadvantage; consequently the sublevel caving process is lengthy and the coal arches over the small opening leading to stoppage of the work. A further significant drawback of the described equipment is that there is not sufficient space for the handling crew, i.e. no clear access can be provided. A further drawback is that the coal falling down at the caving-side end of the equipment can no longer be loaded onto the conveyor, resulting in fairly high losses. In addition such equipment has several other technical and economic deficiencies.
In the other system for sublevel caving technology, the roof plate has a swinging extension bending down backwards externally into the caving. The second conveyor is below this extension. The deficiencies and drawbacks are nearly the same as those described above. Here the open position of the second conveyor is even more disadvantageous. Its repair and maintenance are nearly impossible and dangerous, since the work in the caving must be carried out at places practically without protection.